[Feature] Added convert base function.

Author: exterkamp

README.md

@@ -73,6 +73,7 @@ Different algorithmic programs.  Grouped by general topic.
 #### Mathematical Algorithms
 * [Fibonacci](algorithms/math/fibonacci.py)
 * [Factorial](algorithms/math/factorial.py)
+* [Convert Base](algorithms/math/convert_base.py)
 
 #### String Based Algorithms
 * [Fizz Buzz](algorithms/string/fizz_buzz.py)

algorithms/math/convert_base.py

@@ -0,0 +1,17 @@
+def convert_base(val: str, base: int):
+    if base < 0 or (base > 10 and base !=16):
+        return -1
+    value = 0
+    for i, digit in enumerate(val):
+        digit_val = convert_digit_to_int(digit)
+        if digit_val < 0 or digit_val > base:
+            return -1
+        # print(digit_val, base ** (len(val)-i-1))
+        value += digit_val * (base ** (len(val)-i-1))
+    return value
+
+
+def convert_digit_to_int(char: str):
+    if len(char) != 1 or ord(char) > ord('f'):
+        return -1
+    return int(char,16)

tests/test_convert_base.py

@@ -0,0 +1,31 @@
+import unittest
+from algorithms.math.convert_base import convert_base, convert_digit_to_int
+
+class TestConvertBase(unittest.TestCase):
+
+    def test_convert_digit_valid(self):
+        for i in range(10):
+            self.assertEqual(i, convert_digit_to_int(str(i)))
+        for c,v in [('a',10),('b',11),('c',12),('d',13),('e',14),('f',15)]:
+            self.assertEqual(v, convert_digit_to_int(c))
+        for c in 'ghijklmnopqrstuvwxyz':
+            self.assertEqual(-1, convert_digit_to_int(c))
+
+    def test_convert_base_2(self):
+        self.assertEqual(5, convert_base('101',2))
+        self.assertEqual(11,convert_base('1011',2))
+
+    def test_convert_base_10(self):
+        self.assertEqual(20, convert_base('20',10))
+        self.assertEqual(135, convert_base('135',10))
+        self.assertEqual(7, convert_base('7',10))
+    
+    def test_convert_base_16(self):
+        self.assertEqual(int('4e',16), convert_base('4e',16))
+    
+    def test_convert_base_outside_range(self):
+        self.assertEqual(-1, convert_base('63',4))
+    
+    def test_convert_base_invalid_base(self):
+        self.assertEqual(-1, convert_base('101',-3))
+        self.assertEqual(-1, convert_base('101', 12))